Centrifugal casting apparatus with special feed means



March 5, 1968 3,371,705

CENTRIFUGAL CASTING APPARATUS WITH SPECIAL FEED MEANS V. GHIORZO ET AL Filed April 14, 1965 INVENTORS: r/rroz/a G/l/OR'ZW Flam/(5:60 6/1/0420 MZa-l J'- rfii/o ATTORNEY United States Patent Ofifice 3,371,705 Patented Mar. 5, 1968 ABSTRACT OF THE DISCLOSURE The casting arm of a centrifugal casting machine for precious metals carries a crucible which has a melting chamber serving to accommodate a charge of metal. When the casting arm is held in a position of rest and the charge is caused to melt, molten metal fills a lower region of the melting chamber. Such lower region communicates with the inlet of a tunnel through which the metal is expelled into the cavity of a mold when the casting arm rotates. The outlet of the tunnel is located at a level above the inlet so that molten metal seals the open top of the melting chamber from the outlet of the tunnel when the casting arm is held in the position of rest.

This is a continuation-in-part of our copending application Ser. No. 414,148, filed on Nov. 27, 1964.

The present invention relates to casting crucibles, and more particularly to improvements in crucibles which are utilized for melting and casting of platinum or other precious metals. Still more particularly, the invention relates to casting crucibles Which may be used with advantage in all types of centrifugal casting machines, especially in centrifugal casting machines of the type disclosed in our aforementioned copending application Ser. No. 414,148.

Known casting crucibles wherein platinum is melted by a torch define a melting chamber which may receive a charge of metal and which is surrounded by heat-resistant material so that the charge in the chamber may be heated to a temperature which is above the melting point. The crucible has an evacuating passage through which molten material is expelled by centrifugal force to enter the cavity of a mold when the mold and the crucible are mounted in a centrifugal casting machine. A serious drawback of such casting crucibles is that the evacuating passage is located at a level above the surface of molten metal when the crucible is held in a horizontal position so that hot and cool air, soot, and other combustion products and impurities may enter the mold cavity at all times, i.e., not only while the charge is being heated to melting temperature but also subsequent to melting and until the centrifugal casting machine is set in motion. The flow of air through the evacuating passage is highly undesirable, not only because the mold cavity might receive solid or gaseous contaminating matter but also because, during casting (i.e., while the charge of molten material enters the mold cavity in response to the action of centrifugal force), some air will flow through the passage and will penetrate into molten material to form air bubbles which remain entrapped in the casting. It is clear that a casting with air bubbles entrapped therein is of inferior quality.

Accordingly, it is an important object of the present invention to provide a novel and improved casting crucible for use in centrifugal casting machines and to construct the crucible in such a way that the cavity of the mold is sealed from the melting chamber, at least at such times when the charge of metal which was admitted into the chamber has been heated to a temperature above the melting point and while the crucible remains in a horizontal position.

Another object of the present invention is to provide a casting crucible of the just outlined characteristics which may be utilized with equal advantage in conventional centrifugal casting machines as well as in machines which are disclosed in our aforementioned copending application Serial No. 414,148.

A further object of the invention is to provide a casting crucible which automatically prevents flow of air between its melting chamber and the mold cavity as soon as the charge of precious metal melts, and which continues to seal the chamber from the mold cavity when the crucible orbits about a fixed axis to subject the charge of molten material to the action of centrifugal forces and to expel such material into the cavity of the mold.

An additional object of the invention is to provide a casting crucible which embodies the above-outlined features and advantages and which may be produced in any desired size or shape, which may discharge molten metal into many types of existing molds, which can be produced at low cost of many known heat-resistant materials, and which is just as long-lasting as any presently used conventional crucibles.

Still another object of the present invention is to provide a centrifugal casting machine which can utilize a casting crucible of the above outline characteristics.

A concomitant object of the invention is to provide a centrifugal casting machine which utilizes the improved casting crucible and wherein the charge of precious metal may be heated when the machine is in operation and/ or when the machine is idle.

Briefly stated, one feature of our invention resides in the provision of an improved casting crucible which is particularly suited for melting of platinum or other precious metals and which, when mounted in a centrifugal casting machine, may be used to discharge a predetermined quantity of molten metal into the cavity of a mold. The crucible consists of heat-resistant material and defines a melting chamber preferably bounded by a concave bottom wall and having an open top so that it may receive and accommodate a supply of metal to be melted whereby, upon melting, such metal fills the chamber to a predetermined level. The crucible further defines an evacuating passage having an inlet portion which is located entirely below the level of molten metal and which communicates with the melting chamber, and an outlet portion which is located above the level of molten metal so that such molten metal prevents the flow of air between the melting chamber and the outlet portion of the evacuating passage. The outlet portion may be placed adjacent to the intake end of a channel leading to the mold cavity and, whenthe crucible and the mold are rotated as a unit about a fixed horizontal or vertical axis, with the crucible located between the axis and the mold and the passage located between the mold cavity and the melting chamber, molten metal will be compelled to How through the passage and will fill the mold cavity.

As a rule, the charge of metal which is placed into the melting chamber is heated by a jewelers torch while the crucible remains in a horizontal or nearly horizontal position, i.e., in such position that the open side of the melting chamber faces upwardly and the inlet portion of the passage is located below the level to which the chamber is filled with metal once the charge is heated to a temperature above the melting point. As disclosed in our copending application Serial No. 414,148, the torch may be mounted in such a way that it can rotate with the crucible and continues to heat the molten mass while the latter is subjected to the action of centrifugal forces and is caused to penetrate into the mold cavity.

The crucible may consist of any suitable refractory material which can withstand temperatures at least slightly exceeding the melting point of the metal which is being cast.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved casting crucible itself, however, both as to its construction and the mode of utilizing the same, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a crucible which embodles our invention, a portion of a jewelers torch being shown in operative position in which the flame can heat a charge of platinum or other precious metal in the melting chamber of the crucible;

FIG. 2 is a longitudinal vertical section through the crucible, substantially as seen in the direction of arrows from the line II-II of FIG. 3;

FIG. 3 is a horizontal section through the crucible, substantially as seen in the direction of arrows from the line III-III of FIG. 2;

FIG. 4 is a vertical section similar to that of FIG. 2 and illustrates the crucible in a different angular position; and

FIG. 5 illustrates a centrifugal casting machine which may utilize the crucible shown in FIGS. 1 to 4.

Referring first to FIG. 1, there is shown a crucible 1 which consists of sand, clay, graphite or other suitable heat-resistant material. The left-hand portion of the crucible defines a melting chamber 2 which is bounded by a concave bottom wall and has an open top, shown at 3, located below the nozzle or head 5 of a jewelers torch 4 so that an accurately weighed charge of platinum or other precious metal can be melted by the flame and is then ready to be introduced into the cavity 21 of a mold 20 which is shown in FIG. 5.

FIG. 2 shows that the right-hand portion of the crucible 1 defines a specially configurated evacuating passage or tunnel 6 having an inlet portion 7 which is located entirely below a predetermined level 8 indicating the exposed surface of molten metal 9 which is obtained in response to melting of the accurately weighed charge in the chamber 2. The outlet portion 10 of the passage 6 is located above the level 8 so that, and as shown at 11, molten material 9 can penetrate into and seals the inlet portion 7 whereby the chamber 2 cannot communicate directly with the outlet portion 10. This prevents air from entering the mold cavity 21 when the charge has been heated to a temperature which is above the melting point.

Referring to FIG. 3, it will be seen that the width of the passage 6 may diminish gradually in a direction from the chamber 2 toward the outlet portion 10. FIG. 2 shows that the height of the passage 6 may increase in the same direction, i.e., from the chamber 2 toward the outlet portion 10. For example, the minimum height of the inlet portion 7 may be about 5 mm.

The charge which is introduced into the chamber 2 is melted while the base 13 of the crucible 1 is held in a horizontal or substantially horizontal position as shown in FIGS. 1 and 2. When the entire charge melts and the resulting molten material 9 fills the chamber 2 up to the level 8, a portion of the passage 6 between the chamber 2 and the outlet portion 10 is sealed by molten metal. The crucible is then caused to rotate at a high speed and with rapid acceleration, for example, in the direction indicated in FIG. 2 by the arrow 12, and about a fixed hori zontal axis which is located to the left of the crucible, as viewed in FIGS. 1 to 3. It will be noted that the chamber 2 is located between the fixed axis and the passage 6, and also that the outlet portion 10 of the passage 6 is located at a maximum distance from the fixed axis. The cavity 21 of the mold 20 shown in FIG. 5 is located to the right of the crucible, as viewed in FIGS. 1 to 3, to make sure that molten material 9 escapes through the outlet portion 10 of the passage 6 in response to the action of centrifugal force and fills the mold cavity. When the crucible rotates and travels through an angle of about degrees (as seen in the direction indicated by the arrow 12), it assumes a position which is shown in FIG. 4. It will be seen that, in such position, too, the charge 9 of molten metal fully seals the outlet portion 10 from the chamber 2. The metal escapes from the crucible at a rate determined by the minimum cross-sectional area of the passage 6 and by the rotational speed of the casting arm 15 (see FIG. 5) on which the crucible is mounted, and such metal ultimately fills the mold cavity 21 to form a casting which is allowed to set and is then removed from the mold 20 in a well known manner not forming part of the present invention. The mold cavity 21 communicates with one or more vents, not shown, which allow air to escape from the mold so that the cavity may be completely filled with metal.

In heretofore known casting crucibles, the entire evacuating passage is located above the level of molten metal when the crucible is held in a horizontal position. Therefore, hot and cold air, soot, other combustion products and similar undesirable impurities can enter the mold cavity not only while the metal is heated to melting temperature but also after the metal has been transformed into a mass of molten material. In such crucibles, air bubbles are likely to form in the casting which, of course, is highly undesirable. The formation of such bubbles is due to the fact that, at least in the initial stage of the casting operation, i.e., when the crucible begins to rotate about a fix d axis, some air will flow through the passage toward the mold cavity or in the opposite direction and will penetrate into molten material. Since the improved crucible has a passage 6 a portion of which is invariably filled with molten metal, even when the crucible is held in horizontal position, such penetration of air into the mass of molten metal is not only unlikely but practically impossible.

FIG. 5 illustrates a portion of a centrifugal casting machine of the type disclosed in our copending application Serial No. 414,148 but utilizing a crucible 1 of the type shown in FIGS. 1 to 4. This casting machine comprises an elongated casting arm '15 which resembles a scale beam and is rotatable about the axis of a horizontal drive member here shown as a shaft 16. The shaft 16 may be driven by suitable drive means, for example, by a spring motor which is accommodated in a housing 17 supported by legs 18. A spring motor which may be used in the machine of FIG. 5 is disclosed in our copending application Serial No. 414,148. The right-hand portion of the arm 15, as viewed in FIG. 5, extends radially of the shaft 16 and carries a platform 19 which supports the crucible 1 and a composite mold 20 having a cavity 21 connected with the outlet portion 10 of the passage 6 by a channel 22. The arrow 12 indicates the direction in which the motor can drive the shaft 16 to orbit the crucible 1 and mold 20 about a fixed horizontal axis.

The torch 4 comprises a conduit 23 which is supported by a bracket or post 24 mounted on the platform 19.

The heating device which includes the torch 4 further comprises a source of combustible material here shown as including an oxygen tank 25, an acetylene tank 26, a mixer or manifold 27, a first valve 28 which controls the discharge of oxygen into the conduit 23, and a second valve 29 which controls the flow of acetylene from the tank 26. In the machine of FIG. 5, the tanks 25, 26 are mounted on the left-hand portion of the arm 15 and constitute a counterweight to balance the weight of the platform 19, of the parts which are mounted on this platform, and of the bracket 24. The nozzle 5 of the torch 4 directs the flame through the open top 3 of the melting chamber 2 so as to melt an accurately weighed charge of platinum or another precious metal which is placed into the crucible 1. The level of molten mass is indicated at 8 and, when the arm 15 is held in a position of rest,

the level 8 is located below the outlet portion of the passage 6.

It will be readily understood that the crucible of our present invention may be used with equal advantage in other types of centrifugal casting machines which are disclosed in our copending application Serial No. 414,148, as well as in conventional casting machines wherein the charge is not heated when the crucible rotates, i.e., wherein the charge in the melting chamber of the crucible is heated only while the machine is idle.

It will be seen that the improved crucible is a one-piece body comprising two portions or sections which are located side-by-side while the crucible is maintained in the horizontal position shown in FIGS. 1 to 3 and 5. One of these sections or portions defines the melting chamber 2 and the other portion defines the passage or tunnel 6.

Without further analysis, the foregoing will so fully reveal the gist of the presentinvention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a centrifugal casting machine, particularly for casting of precious metals, drive means comprising a rotary drive member, a casting arm secured to and extending substantially radially with reference to said drive member, said casting arm having a position of rest; a crucible fixed to said arm and spaced from'said drive member, said crucible consisting of heat-resistant material and defining a melting chamber having an open top and adapted to accommodate a supply of precious metal whereby, when such metal is melted and when said arm is maintained in said position of rest, molten metal fills a lower region of said chamber, said crucible further defining an evacuating tunnel having an inlet portion communicating with said lower region of said chamber and an outlet portion, the top of said inlet portion being located below the bottom of said outlet portion when the arm is maintained in said position of rest so that molten metal seals said open top of the melting chamber from said outlet portion, said melting chamber being located intermediate said tunnel and said drive member; means for heating the metal in said chamber; and a mold mounted on said arm and defining a cavity which communicates with said outlet portion, said crucible being located between said drive member and said mold so that, when the casting arm is caused to rotate, centrifugal force compels molten metal to flow through said tunnel and to accumulate in said cavity.

2. In a centrifugal casting machine, particularly for casting of precious metals, drive means comprising a rotary drive member; a casting arm secured to and extending substantially radially with refernce to said drive member, said casting arm having a position of rest; a tending substantially radially with reference to said drive member, said crucible consisting of heat-resistant material and defining a melting chamber having an open top and adapted to accommodate a supply of precious metal whereby, when such metal is melted and when said arm is maintained in said position of rest, molten metal fills a lower region of said chamber, said crucible further defining an evacuating tunnel having an inlet portion communicating with said lower region of said chamber and an outlet portion, the top of said inlet portion being located below the bottom of said outlet portion when the arm is maintained in said position of rest so that molten metal seals the open top of the melting chamber from said outlet portion, said melting chamber being located intermediate said tunnel and said drive member; heating means including a jewelers torch mounted on and rotatable with said arm, said torch having a nozzle arranged to direct a flame through the open top of said chamber; and a mold mounted on said arm and defining a cavity which communicates with said outlet portion, said crucible being located between said drive member and said mold so that, when the casting arm is caused to rotate, centrifugal force compels molten metal to flow through said tunnel and to accumulate in said cavity.

3. In a centrifugal casting machine, particularly for casting of precious metals, drive means comprising a rotary drive member; a casting arm secured to and extending substantially radially with reference to said drive member said casting arm having a position of rest; a crucible fixed to said arm and spaced from said drive member, said crucible consisting of heat-resistant material and defining a melting chamber having an open top and adapted to accommodate a supply of precious metal whereby, when such metal is melted and when said arm is maintained in said position of rest, molten metal fills a lower region of said chamber, said crucible further defining an evacuating tunnel having an inlet portion communicating with said lower region of said chamber and an outlet portion, the top of said inlet portion being located below the bottom of said outlet portion when the arm is maintained in said position of rest so that molten metal seals the open top of the melting chamber from said outlet portion, said melting chamber being located intermediate said tunnel and said drive member; means for heating the metal in said chamber; a mold mounted on said arm and defining a cavity which communicates with said outlet portion, said crucible being located between said drive member and said mold so that, when the casting arm is caused to rotate, centrifugal force compels molten metal to flow through said tunnel and to accumulate in said cavity; and counterweight means mounted on said drive member substantially diametrically opposite said crucible and said mold.

4. In a centrifugal casting machine, particularly for casting of precious metals, drive means comprising a drive member arranged to rotate about a horizontal axis; a casting arm secured to and extending substantially radially with reference to said drive member, said casting arm having a position of rest; a crucible fixed to said arm and spaced from said drive member, said crucible consisting of heat-resistant material and defining a melting chamber having an open top and adapted to accommodate a supply of precious metal whereby, when such metal is melted and when said arm is maintained in said position of rest, molten metal fills a lower region of said chamber, said crucible further defining an evacuating tunnel having an inlet portion located entirely below said level and an outlet portion, the top of said inlet portion being located below the bottom of said outlet portion when the arm is maintained in said position of rest so that molten metal seals the open top of the melting chamber from said outlet portion, said melting chamber being located intermediate said tunnel and said drive member; means for heating the metal in said chamber; and a mold mounted on said arm and defining a cavity which communicates with said outlet portion, said crucible being located between said drive member and said mold so that, when the casting arm is caused to rotate, centrifugal force compels molten metal to flow through said tunnel and to accumulate in said cavity.

5. In a centrifugal casting machine, particularly for casting of precious metals, drive means comprising a rotary drive member; a casting arm secured to and extending substantially radially with reference to said drive member, said casting arm having a position of rest; a crucible fixed to said arm and spaced from said drive member, said crucible consisting of heat-resistant material and defining a melting chamber having an open top and adapted to accommodate a supply of precious metal whereby, when such metal is melted and when said arm is maintained in said position of rest, molten metal fills a lower region of said chamber, said crucible further defining an evacuating tunnel having an inlet portion communicating with said lower region of said chamber and an outlet portion, the top of said inlet portion being located below the bottom of said outlet portion when the arm is maintained in said position of rest so that molten metal seals the open top of the melting chamber from said outlet portion, said melting chamber being located intermedi ate said tunnel and said drive member; means for heating the metal in said chamber; and a mold mounted on said arm and defining a vented cavity which communicates with said outlet portion, said crucible being located between said drive member and said mold so that, when the casting arm is caused to rotate, centrifugal force compels molten metal to flow through said tunnel and to accumulate in said cavity.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 3 /1922 Switzerland.

WILLIAM J. STEPHENSON, Primary Examiner.

R. S. ANNEAR, Assistant Examiner. 

